Stent design properties and deployment ratio influence indexes of wall shear stress: a three-dimensional computational fluid dynamics investigation within a normal artery

Abstract

Restenosis limits the effectiveness of stents, but the mechanisms responsible for this phenomenon remain incompletely described. Stent geometry and expansion during deployment produce alterations in vascular anatomy that may adversely affect wall shear stress (WSS) and correlate with neointimal hyperplasia. These considerations have been neglected in previous computational fluid dynamics models of stent hemodynamics. Thus we tested the hypothesis that deployment diameter and stent strut properties (e.g., number, width, and thickness) influence indexes of WSS predicted with three-dimensional computational fluid dynamics. Simulations were based on canine coronary artery diameter measurements. Stent-to-artery ratios of 1.1 or 1.2:1 were modeled, and computational vessels containing four or eight struts of two widths (0.197 or 0.329 mm) and two thicknesses (0.096 or 0.056 mm) subjected to an inlet velocity of 0.105 m/s were examined. WSS and spatial WSS gradients were calculated and expressed as a percentage of the stent and vessel area. Reducing strut thickness caused regions subjected to low WSS (<5 dyn/cm(2)) to decrease by approximately 87%. Increasing the number of struts produced a 2.75-fold increase in exposure to low WSS. Reducing strut width also caused a modest increase in the area of the vessel experiencing low WSS. Use of a 1.2:1 deployment ratio increased exposure to low WSS by 12-fold compared with stents implanted in a 1.1:1 stent-to-vessel ratio. Thinner struts caused a modest reduction in the area of the vessel subjected to elevated WSS gradients, but values were similar for the other simulations. The results suggest that stent designs that reduce strut number and thickness are less likely to subject the vessel to distributions of WSS associated with neointimal hyperplasia.

Sequential Structural and Fluid Dynamics Analysis of Balloon-Expandable Coronary Stents: A Multivariable Statistical Analysis

“…These computational methods of analysis employ sophisticated numerical techniques, such as the finite element and finite volume methods, to obtain approximate numerical solutions to complex physical problems. To date, a large number of studies have carried out computational structural (CS) analyses 1,4,5,14,15,19,[25][26][27][28][29]37,44,53,54,57,59,[62][63][64]72,73,78,80,85,87,[90][91][92] and computational fluid dynamics (CFD) analyses 3,8,9,12,30,31,33,42,[47][48][49][50][51]65,66,69,[74][75][76]83,89 ...…”

Numerical investigation of pulsatile flow in endovascular stents

“…This work was extended by LaDisa et al 18 by first considering the effect of the difference in the stent diameter with respect to the vessel diameter, and also changing the number of stent struts and the wire thickness. The inflow condition was a steady parabolic profile with a mean value corresponding to the time-averaged flowrate of a characteristic waveform for a human vessel.…”

“…When four stent struts in a cross section were used, the cross section after stent implantation was polygonal (instead of circular); when eight struts were used, however, the cross-section was almost circular. Following LaDisa et al 18 the difference between the effective stent diameter and that of the vessel was considered. An unsteady velocity profile was imposed at the inlet, and the flow was allowed to develop over an extended entrance length.…”

Microfocal X-ray computed tomography post-processing operations for optimizing reconstruction volumes of stented arteries during 3D computational fluid dynamics modeling

“…Distributions of WSS in the theoretical and high frequency spatial error arteries were determined after imposing a steady-state inlet velocity of 24 mm/s (Re = 17) similar to that used at the inlet of the reconstructed iliac arteries. Theoretical arteries in the absence and presence of high frequency spatial error were then subjected to the surface smoothing techniques described above and distributions of WSS were obtained as previously described 3,4 . Development of regional neointimal hyperplasia within the stented portion of an artery may introduce localized geometric asymmetry.…”

“…Computational modeling of regional blood flow through normal or diseased arterial segments requires highly accurate representations of vascular geometry. Our laboratory has conducted several investigations examining theoretical alterations in WSS produced by stent implantation using 3D computational fluid dynamics (CFD) modeling 3,4 . These data suggest that stent design plays an important role in the distribution of low WSS that has been previously correlated with neointimal hyperplasia.…”